To profit by selling defective RAM chips that should have never been allowed to leave the factory.
Defective RAM is RAM that does not work. Operational voltage has nothing to do with it. If it did, then what does that make 1.35v DDR3?
But it is wrong for a memory manufacturer to state that their product which runs at 1.65V is P67 Platform Ready. Its really not. 1.65V memory is last generation memory.
Does any one remember when DDR3 first came out for the higher end socket 775 platform? There were kits on the market that were rated at 1.8v - yes, DDR3 and not DDR2!
Intel allows for a 10% voltage deviation on their IMC. "P67 ready" is just a marketing term, since in theory any memory within Intel's allowed voltage of 1.65v and otherwise following JEDEC specifications should work with anything from X58 to P67.
Memory IC (not to be confused with memory module) manufacturers will rate for 1.5v because that is the JEDEC standard.
Note that manufacturers of other computer components will vary voltage as needed. For instance, even Intel varies the voltage their CPUs require - some require more and some require less.
Memory modules sold at a voltage higher than 1.5v is marketing to overclockers and enthusiasts. In the past memory was sold at the nominal JEDEC standard. Then, overclockers figured out that more voltage = higher clocks. However, not all modules could go faster. Memory module manufacturers just capitalized on this by pre-testing (AKA binning) modules so the ones capable of higher speeds can be sold at a premium because they were better (AKA guaranteed).
Of course it is now getting a bit out of hand because I've seen even mediocre DDR3-1333 with higher voltage, but still that has nothing to do with anything being "defective" or "last generation."
This all being said, as I've recommended countless times before, buy 1.5v DDR3. Especially with Sandy Bridge, there is no benefit to buying expensive RAM. Just buy cheap $40-for-4GB DDR3-1333 at 1.5v.